This invention relates to a polyimide precursor, a process for producing the polyimide precursor, a polyimide, a process for producing the polyimide, a photosensitive composition, a process for using the photosensitive composition in the production of semiconductor devices, etc., and a semiconductor device and production thereof.
In semiconductor industry, inorganic materials have been used as interlaminar insulating materials. But recently, organic materials having excellent heat resistance such as polyimide resins and the like are used as interlaminar insulating materials by using their properties.
On the other hand, semiconductor integrated circuit pattern formation and circuit pattern formation on printed circuit substrates are carried out by various complicated steps, for example, forming a film of resist material on a substrate, exposing predetermined portions to light, removing unnecessary portions by etching and the like, cleaning the substrate surface, etc. In such a process, it is desirable to use a resist on necessary portions as it is as an insulating material after the pattern formation by exposure to light and development. Thus, the development of heat resistant photosensitive materials for such a purpose are demanded.
In order to meet such a demand, there are proposed heat resistant photosensitive materials using photosensitive polyimides, ring-closed polybutadienes, etc. as base polymers. Particularly the photosensitive polyimides are noticed due to excellent heat resistance and easiness of removable of impurities.
For example, JP-B 49-17374 proposed a material comprising a polyimide precursor and a bichromate. This material had advantages in practical photosensitivity and high film-forming ability, but also disadvantages in storage stability and retention of chromium ions in the polyimide. Thus, such a material was not used practically.
In order to avoid such problems, JP-A 54-109828 proposed a process for mixing a compound having a photosensitive group with a polyimide precursor. Further, JP-A 56-24343 and JP-A 60-100143 proposed processes for providing photosensitive groups by reacting a functional group in a polyimide precursor with a functional group in a compound having a photosensitive group. These photosensitive polyimide precursors use as a fundamental skeleton an aromatic monomer which is excellent in heat resistance and mechanical properties. But due to absorption of the polyimide precursors per se, light transmittance in the ultraviolet region becomes low and photochemical reaction on exposed portions is not carried out sufficiently effectively, resulting in providing problems such as low sensitivity and worsened pattern shape.
With recent tendency of higher integration of semiconductors, higher resolution (or smaller processing rule) is also demanded.
In order to meet such a demand, a contact/proximity exposing device using a parallel light previously used is going to be replaced by a 1:1 projection exposing device which is called by "a mirror projection", or a so-called "stepper" which is a reducing projection exposing device.
The stepper uses a high output oscillation line of ultra-high pressure mercury lamp and monochromatic light such as excimer laser light. As the stepper, a g-line stepper which uses a visible light (wavelength 435 nm) of g-line of ultra-high pressure mercury lamp was used mainly. But in order to meet the demand for higher resolution, it is necessary to make the wavelength used in the stepper shorter. Thus, the g-line stepper (wavelength 435 nm) is going to be replaced by an i-line stepper (wavelength 365 nm).
On the other hand, known photosensitive polyimide are designed for the contact/proximity exposing device, the mirror projection exposing device, and the g-line stepper. But such polyimides are low in transparency and show almost no transmittance when the i-line (wavelength 365 nm) is used. Therefore, no sufficient pattern can be obtained when the i-line stepper is used.
Further, in order to meet the LOC (lead on chip) wherein a high density mounting method of semiconductor is used, a polyimide film for surface protection is required to have a thicker film thickness. When the film thickness becomes larger, the problem of low transmittance becomes severer.
Furthermore, a diameter of a silicon wafer becomes larger every year. To the contrary, a thickness of a silicon wafer has a tendency to become smaller. On the other hand, a thickness of a polyimide film becomes larger every year due to the mounting method mentioned above. Accordingly, a warp of a silicon wafer having a polyimide surface protective film thereon is occured due to the difference of thermal expansivity between the polyimide film and the silicon wafer. Therefore, a photosensitive polyimide having lower thermal expansivity is strongly required.